Electric discharge lamp



April 1951 E. H. NELSON ET AL 2,549,328

ELECTRIC DISCHARGE LAMP Filed A rii 15, 1946 INVENTORS'. EVAN H. NELSON,ERNEST B. POWER,

THEIR ATTORNEY Patented Apr. 17, 1951 ELECTRIC DISCHARGE LAMP EvanHerbert Nelson, Harrow Weald, and Ernest Benjamin Power, Kenton,England, assignors to General Electric Company, a corporation of NewYork Application April 13, 1946, Serial No. 662,032 In Great BritainMarch 5, 1945 Section 1, Public Law 690, August 8, 1946 Patent expiresMarch 5, 1965 5 Claims. (01. 116- 126) The present invention relates toelectric dis- '7 charge lamps of the type having quartz envelopes andparticularly, but not exclusively to high pressure mercury vapour lamps.The present invention is concerned with the'basing of electric dischargelamps.

.ample with reference to The electric discharge lamps, bases haveusually to perform two functions, namely (1) To provide convenient meansfor introducing current into the lamps;

(2) To protect the leads and seals of the lamps and improve theirappearance. e

The usual method of attaching bases to lamps is to use a cement capableof cementing the base material, which is usually brass, to the materialof the lamp envelope. In discharge lamps without an outer envelope,surrounding the quartz .envelope of the lamp proper, this method is notusually convenient as it is diflicult to form the quartz into a shapefavourable to receiving a cemented base, moreover it is generallydesirable that the lamps should be as small as possible, in-which .casethe base must be close to the discharge path Within the envelope and itis then difficult or impossible to obtain a cement which .will withstandthe high temperature, which may for example be about 300 C., and alsohave the other required properties. 7

It is the object of the present invention to provide an electricdischarge lamp in which these difficulties are avoided.

According to the present invention, an electric discharge lamp comprisesa quartz stem tube open at one end and closed at the other end, ahermetically closed quartz envelope fixed to said tube in such a mannerthat the open end thereof lies outside the envelope, at least oneelectrode within said envelope, connecting means, such as a base havingone or more terminals connected to said electrode or electrodes andsecuring means for attaching said connecting means to said quartz tube,the said securing means comprising a compressible refractory material,such as asbestos, within the said tube and a member passing through thesaid refractory material and serving to expand this material outwardsagainst the inner wall of said tube.

The said member may comprise a threaded bolt provided with a nut,preferably of conical shape, the bolt being tightened on to the nut andthus exerting pressure upon the said refractory material in a directionparallel to the axis of the tube and causing it to expand outwardsagainst the inner wall of the tube.

the accompanying drawing in which:

Fig. 1 is a view in sectional elevation of part of one embodiment of theinvention applied to a lamp having two electrodes and two seals at op- Vposite ends, and.

Figs. 2 and 3 show in-sectional elevation and underside plan viewsrespectively the way in which the embodiment of Fig. 1 can be applied toa lamp having two electrodes and o ly 9I e seal at one end thereof. Inthe view of Fig.3 the lamp base has been removed.

Fig. 4 is a fragmentary sectional elevation of the end portion of thequartz tube andthe parts attached thereto, similar to that shown in Fig.2, and turned .90 from the position of Fig. 2, and

Fig. 5 is a sectional view along the line.5-5 of Fig. 2 turned 90 andshowing a modificationof the tube.

Referring to Fig. 1, a hermetically closed lamp envelope II] has withinit two electrodes II and [2. Since the arrangement of seals for thesetwo electrodes is identical only one, namely that for the electrode II,is shown. The electrode ll passes out through a quartz neck l3 to theend of which is sealed the' closed end of a relatively thick-Walledquartz tube l4. One or more molybdenum strips l5 having one endconnected to the electrode II are embedded in the wall of the quartztube [4 and pass to the outside at a shoulder [6 near the end of thetube remote from the envelope where the tube diameter is stepped down toa smaller size. Within the bore of the tube is placed a tube of asbestosI! and over the end of the tube is arranged an aperturedmetal plate l8,for instance of brass, which may be circular. A threaded bolt I9 ispassed through the metal plate l8 and asbestos tube I1 and engages in anut '20 of conical shape having its smaller diameter facing inwards andbearing on the asbestos tube. The bolt is tightened and the compressionof the asbestos and the action of the conical nut causes the asbestostube to expand against the inner wall of the quartz tube l4 and causesthe metal plate l8 to be drawn firmly up against the open end of thequartz tube. In order to protect the seal, a tube 2|, for example ofbrass, may be arranged around the seal and soldered at one end to themetal plate l8, theopposite end bearing againstthe quartz envelope. Theouter ends of the molybdenum strip or strips l5 may be soldered to themetal plate I8 which then constitutes a terminal contactfor the lamp. Ametal The invention will be described by way of exbase may beplacedover'the end ofthe head of molybdenum strips 15 are embedded inthe quartzv tube in diametrically opposite positions as an be seen fromFig. 3. e

The metal plate It is, in this case made of elongated shape wherebythetwo molybdenum strips can pass on either sideof it and remaininsulated from it. A metal tube 2| 'is arranged as before and solderedto the metal plate 18 and a cap 22, which may be of the normal kind andof brass, is soldered over the end of the metal tube 2|. The molybdenumstrips, 15 aresoldered to two external contacts 23 and 23 .(Figs; 2 and4) mounted on the base, insulated from one another and from the base. 22may constitute onecontact in which one of the molybdenum strips issoldered thereto and only one insulated contact 23 is provided.-

The asbestos tube or plug 11 may be painted with or soakedinconcentrated sodium silicate to improve its adhesion to the quartz andprevent slipping.

The bore of the quartz tube l4 maybe made of {other than circularcross-section, for example, it may be a polygon" as shown at 24 in Fig.5 or niay be'provided'with a local deformation, such as a longitudinallyextending rib shown at 25 in Fig. 4 to prevent rotation of the asbestosplug l'l therein.

We claim:

1. An electric discharge lamp designed for operation at elevatedtemperatures comprising a refractory vitreous envelope having anelectrically conducting seal comprising a refractory vitreous tube openat its end remote from the lamp envelope, terminal means forelectrically connecting said lamp to a power source and means forholding said terminal means on said tube, .said holding means includinga compressible refractory material positioned in said tube, a plateacross the open end of said tube and supporting said terminal means, abolt extending through said plate and said material into said tubewithits head engaging said plate and-a nut on the inner end of said boltpressing said material against said plate and into frictional engagementwith quartzenvelopehaving a discharge supPOrting 4 the inner wall ofsaid tube to hold said terminal means on'said lamp.

,2. An electric discharge lamp according to claim 1, wherein the bore'of said tube is of noncircular cross-sectional shape to preventrotation of said compressible material therein.

3. An electric discharge lamp according to with a local deformation toprevent rotation of said compressible material therein.

4. vA-n electric discharge lamp according to claim 1 wherei-nsaidcompressible material is asbestos including a substance which improvesits adhesion to said tube; V

'5. An electric discharge lamp comprising a electrodesealed therein, aquartz'tube protruding Alternatively the cap from said envelope with itsinner end closed and its outer end open, an electrical conductorconnected to said electrode, extending longitudinally of said" tube,embedded in the tube wall and emerging from said tube adjacent its openend, a terminal contact for said lamp electrically connected to saidconductor and means for securing said contact on said tube, said meanscomprising a metal plate over theopen end of said tube and supportingsaid terminal contact, a bolt passing through an opening in said plateand into the bore of the tube, an asbestos plug around said bolt and anut on the inner end of said bolt pressing said plug against said plateand into frictional engagement with the inner Wall of said tube to holdsaid terminal contact on said lamp.

EVAN HERBERT NELSON. ERNEST BENJAMIN POWER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Great Britain July 14, 1943

